If a potential candidate tried to tell me that they had no problem and even enjoyed working 20 hours a day, I wouldn't hire them because they are demonstrating that they are clearly incapable of basic organizational skills.
Or the candidate may have just failed another interview hours ago because he said he enjoyed working 8 or 12 hours a day, and lose the faith of humanity all together.
You'll never know why they've generated that answer if you don't ask a follow up question.